# AP Board 10th Class Physical Science Notes Chapter 3 Refraction of Light at Plane Surfaces

Students can go through AP State Board 10th Class Physical Science Notes Chapter 3 Refraction of Light at Plane Surfaces to understand and remember the concept easily.

## AP State Board Syllabus 10th Class Physical Science Notes Chapter 3 Refraction of Light at Plane Surfaces

→ The process of changing speed when light travels from one medium to another medium is called the refraction of light.

→ Absolute refractive index = $$\frac{\text { Speed of light in vacuum }}{\text { Speed of light in medium }}$$ ⇒ n = $$\frac{\mathrm{c}}{\mathrm{v}}$$

→ Relative refractive index, n21 = $$\frac{v_{1}}{v_{2}}=\frac{n_{2}}{n_{1}}$$

→ Snell’s law is given by, n1 sin i = n2 sin r.

→ The angle of incidence at which the light ray travels from denser to rarer medium grazes along the interface is called the critical angle of that interface.
sin C = $$\frac{n_{2}}{n_{1}}$$
where n1 is the refractive index of the denser medium and n2 is the refractive index of the rarer medium.

→ If the angle of incidence is greater than the critical angle, the light ray is reflected into the denser medium at the interface. This phenomenon is called total internal reflection.

→ Example of denser medium: Glass.

→ Example of a rarer medium: Air.

→ When the light travels from rarer to a denser medium, it bends towards the normal.

→ When the light travels from a denser to a rarer medium, it bends away from the normal.

→ Optical fibers work on the principle of total internal reflection.

→ Mirages are formed due to total internal reflection. → The refractive index increases with height.

→ Total internal reflection is the main cause for the brilliance of diamonds.

→ Light travels at a speed of 3 × 108 m/s.

→ The Refractive index depends on the following factors :

• Nature of material
• The wavelength of light used.

→ When the refractive index of glass is $$\frac{3}{2}$$, then the speed of light in glass is equal to 2 × 108 m/s.

→ Laws of refraction :

1. The incident ray, the refractive ray, and the normal interface of two transparent media at the point of incidence lie in the same plane.
2. During refraction, the light follows Snell’s law.

→ A coin kept at the bottom of a vessel filled with water appears to be raised and a lemon kept in the water of glass tumbler appears to be bigger than its size due to refraction of light.

→ Fermat’s principle states that the light ray always travels in a path that needs the shortest possible time to cover the distance between the two points.

→ Speed of light changes at the interface of two media.

→ The angle between the incident and normal ray is called the angle of incidence.

→ The angle between normal and refracted ray is called the angle of refraction.

→ The angle between normal and emergent rays is called the angle of emergence.

→ The formation of mirage is the best example where the refractive index of a medium varies throughout the medium. → Refraction: The process of changing speed when light travels from one medium to another is called the refraction of light.

→ Incident ray: The ray which is an incident on a surface is called an incident ray.

→ Refracted ray: The ray which refracted from a surface is called refracted ray.

→ The angle of Incidence: The angle between the incident ray and normal ray is called the angle of incidence.

→ The angle of Refraction: The angle between refracted ray and normal ray is called the angle of refraction.

→ Absolute refractive index: The ratio of the speed of light in a vacuum to the speed of light in the medium.

→ Relative refractive index: It is the ratio of the refractive index of the second medium to the refractive index of the first medium.

→ Snell’s law: It is the ratio of the sine of the angle of incidence to the sine of the angle of refraction.

→ Critical Angle: The angle of incidence at which the light ray travels from denser to rarer medium grazes along the interface is called the critical angle of that interface.

→ Total internal reflection: When the angle of incidence is greater than the critical angle, the light ray is reflected into the denser medium at the interface. This phenomenon is called total internal reflection.

→ Mirage: Mirage is an optical illusion where it appears that water is collected on the road at a distant place but when we get there, the road is dry.

→ Shift: The distance between incident and emergent parallel rays is called shift.

→ Optical Fibre: An optical fiber is a very thin fiber made of glass (or) plastic having a radius of about a micrometer (10-6 m).

→ Medium: A substance through which light passes is called medium. The medium has more optical density.

→ Denser Medium: The medium which has less optical density.

→ Interface: A point where two things meet and interact is called an interface. → Fermat’s principle: The light ray always travels in a path that needs the shortest possible time to cover the distance between the two given points.

→ The angle of emergence: The angle between normal and emergent rays is called the angle of emergence.

→ Light pipe: A bunch of optical fibers is called a light pipe.

→ Mass density: Mass per unit volume is called mass density.

→ Ray: The straight-line path along which the light travels in a homo¬geneous medium is called a ray. It is represented by an arrowhead on a straight line, the arrowhead gives the direction of propagation of light.

→ Beam: A number of rays combined together are called a beam  Williboard Snell Van Royen (1580 – 1626):

• He was a Dutch astronomer and mathematician.
• His name has been attached to the law of refraction of light.
• In 1815, he planned and carried into practice a new method of finding the radius of the earth by determining the distance of one point from the parallel of latitude of another by means of triangulation.
• He was famous for bis Snell’s law related to the refraction of light.